Process for the manufacture of molded articles

ABSTRACT

PROCESS FOR PREPARING RIGID, IMPACT-RESISTANT ARTICLE COMPRISING A HOLLOW OUTER SHELL COMPONENT AND AN INNER RIGIDIFIER COMPONENT COMRPISING A CELLULAR PLASTIC MATERIAL. THE ARTICLE IS FORMED BY PREPARING SEPARATELY (1) A PREMOLED SKIN FROM A PLIABLE PLASTIC MATERIAL, AND (2) A PLASTIC COMPOSITION HAVING FOAMING CAPABILITY. THE PLASTIC COMPOSITION IS POURED OR SPRAYED INTO A PREMOLDED SHELL COMPONENT AND FOAMS IN PLACE INSIDE THE CAVITY OF THE SHELL COMPONENT. THE RESULTING CELLULAR STRUCTURE IS SOLIDIFIED AND BECOMES RIGID. THE ARTICLE IS RECOVERED.

May 28, 1974 H. ROBERTS PROCESS FOR THE MANUFACTURE OF MOLDED ARTICLESOriginal Filed Jan. 28, 1966 I 4 W7 awwmm liiifr'l" INVENTOR ARTHUR H.ROBERTS o 00.. llllllllllll o o 0 c n W00 5 I. z. I.

United States Patent Office 3,813,462 Patented May 28, 1974 3,813,462PROCESS FOR THE MANUFACTURE OF MOLDED ARTICLES Arthur H. Roberts, 12Lynnwood Drive, Westbury, N.Y. 11590 Division of application Ser. No.760,415, Sept. 18, 1968, which is a division of application Ser. No.523,778, Jan. 28, 1966, now Patent No. 3,419,455, which is aconfinuation-in-part of applications Ser. No. 455,764, May 14, 1965, nowPatent No. 3,405,026, and Ser. No. 475,989, July 30, 1965, now PatentNo. 3,414,456, the latter two being continuations-in-part of abandonedapplication Ser. No. 22,002, Apr. 13, 1960. Divided and this applicationMay 10, 1971, Ser. No. 141,481 The portion of the term of the patentsubsequent to Oct. 7, 1985, has been disclaimed Int. Cl. B29d 27/00 US.Cl. 264-45 23 Claims ABSTRACT OF THE DISCLOSURE Process for preparingrigid, impact-resistant article comprising a hollow outer shellcomponent and an inner rigidifier component comprising a cellularplastic material. The article is formed by preparing separately (1) apremolded skin from a pliable plastic material, and (2) a plasticcomposition having foaming capability. The plastic composition is pouredor sprayed into a premolded shell component and foams in place insidethe cavity of the shell component. The resulting cellular structure issolidified and becomes rigid. The article is recovered.

RELATED APPLICATIONS This application is a division of Serial Number760,415, filed September 18, 1968, which is a division of applicationSerial Number 523,778, filed January 28, 1966, now Patent 3,419,455,which is a continuation-in-part of applications Serial Numbers 455,764,filed May 14, 1965, now Patent 3,405,026 and 475,989, filed July 30,1965, now Patent 3,414,456, which, in turn, are continuation-inpartapplications of application Serial Number 22,002, filed April 13, 1960.Application Number 22,002 has been abandoned.

This invention relates to a process for preparing novel,-

rigid, impact resistant articles. The articles are of varying sizes, mayhave more or less intricate shapes and may have undercuts. Similararticles in the prior art were made predominantly of ceramic or plastermaterials. These prior art articles of manufacture have the disadvantageof being fragile and easily chipped. They require much hand finishing onthe seam lines caused by the mold seams.

The prior art has also disclosed various casting processes formanufacturing seamless hollow articles out of plastisols and similarplastics materials. The resulting product is quite attractive and can bedecorated as easily as plaster, and in fact more easily than ceramics.The plastisol articles so cast will not chip, however they aredeformable. Also, if the die is seamless, a seamless product can beobtained. Plastisol has a defect called creep or cold flow, whichresults in a warpage or distortion at somewhat higher than ambienttemperatures as in the vicinity of household radiators and electriclamps. This property is generally characterized by the temperature atwhich distortion occurs.

Therefore, manufacturers of such prior art articles as lamp bases havehad the choice of producing ceramic and plaster articles or the likewhich are resistant to heat but fragile, or producing plastisol articleswhich have good impact and chipping resistance at normal temperatures,but which are deformable, have cold flow and poor impact resistance atlow temperatures. The phenomenon of cold flow has also been called heatditsortion."

An object of this invention is to provide manufactured articles withimproved properties and without the disadvantages of the prior artarticles.

A further object is to provide a process for producing small and largeseamless objects of plastics with improved resistance to cold flow,chipping and breakage, and which is distinctly superior to prior artprocesses and the products produced thereby.

Other objects of this invention will become apparent from thedescription of this invention further below.

The articles of manufacture of my parent applications are rigid,three-dimensional and hollow. They comprise two components: (1) an outerlayer component, also called the shell and (2) an inner layer component,also called the flesh or rigidifier. In most of the cases varyingparallel cross sections of a single article show varying dimensions andshapes or configurations, indicating curved sidewalls and undercuts. Inother cases the cross sections may be identical, indicating box-shapedor cylindrical ob jects. In an alternative form of said parentapplications the outer layer component and inner layer component jointlyform a cavity and this cavity is then filled with a reinforcing spine,such as a rigid plastics foam material. The outer layer component ismade of a flexible plastics material, illustrated by plastisol andpolyethylene, whereas the inner layer component in the various parentapplications is illustrated for instance by asphalt, plaster of parisand a composition comprising a filler which is bonded by the elastomersolids of a latex.

In contrast to the inventions of the parent applications the compositearticles of manufacture of the instant invention comprise a hollow outershell component and an inner rigidifier component. Further the outershell component is a premolded pliable plastics and has an accessopening. The pliable or flexible nature of the premolded hollow outershell component is characterized by the fact that, when free of therigidifier component, it can be deformed, at least temporarily, by theapplication of hand pressure. In my parent applications the term skinwas used to designate the shell component. The latter expression ispreferred. The inner rigidifier component is a rigid cellular plastics.The rigidifier component is positioned within the space enclosed by theouter shell component and the former is in intimate contact with theentire inner surface of the latter. The rigid cellular plastics may alsobe called rigid plastic foams and may have either a closed cell or anopen cell structure. The closed cell structure is preferred.

The composite articles of manufacture of the instant invention arerigid. In this context the term rigid means a radical increase inrigidity when compared with the outer shell component itself and it alsoindicates utility for purposes requiring at least a certain degree ofrigidity.

The rigid cellular plastics composition according to this invention actsas a rigidifier for the outer shell component. The premolded outer shellcomponent is hollow and the inner rigidifier component may fill thecavity formed by the hollow premolded shell component fully or in part.In the latter case the outer shell and inner rigidifier componentsjointly form a cavity and in such cases a reinforcing spine componentmay be present on the inner surface of the joint cavity. This will bediscussed further below in greater detail.

The varying parallel cross-sections of a single composite article ofmanufacture of this invention may show varying shapes and dimensions,indicating curved sidewalls, angulated sidewalls and undercuts, or mayshow identical shapes and dimensions, indicating box-shaped orcylindrical objects.

The shell is preset in its shape by a molding or forming operation. -Itis formed from a plastics material, which is preferably pliable andresilent. Depending on the plastics material selected to form the shell,the molding operations may vary, in order to utilize the mostadvantageous method for the selected plastics. The outer surface of theshell readily receives coloring materials for decorating the compositearticle. In some cases, such when the shell is of polyethylene, theouter surface may be pretreated prior to decoration. The inner walls ofthe shell define an internal cavity accessible through an opening in theshell. The inner rigidifier component is in intimate contact with theinner walls of the preset shell and is in supporting relationship to theouter shell. This inner component acts as a rigidifier and rigidlymaintains the outer shell in its preset shape. The inner rigidifier isformed by a rigid plastics foam and is described in detail furtherbelow. The rigid foam composition is preferably applied in a liquidstate and solidifies within the preset shell. In a preferred embodimentthe shell component acts as a mold in which to form the inner rigidifiercomponent. Depending on the properties of the shell and the rigid foamcomposition, the setting of the latter may be performed while the shellis in a second mold or die. This second mold or die would usually be asplit mold and is used to prevent deformation of the shell during thecasting and setting of the rigid foam composition forming the innerrigidifier component. The latter acts as a structural rigid backingmember. The use of a second mold is superfluous in many cases.

The outer shell component of the composite article of manufacture ofthis invention has a preferred wall thickness of about $6 of an inch toabout $4 of an inch. Expressed in thousandths of an inch, thiscorresponds to a range of from about 15.625 mils to about 250 mils. Thelower figure may be rounded out to about mils. The inner rigidifierflesh component may have a wall thickness of that equal to the thicknessof the shell, or even be as low as one half of the thickness of theshell, and in many cases the inner rigidifier fills the cavity formed bythe outer layer in full. By varying the formulation of the rigid foamcomposition, a tougher or more rigid inner rigidifier would permit theuse of a thinner layer than a less tough or less rigid inner rigidifier,while maintaining the composition of the shell constant. By changing thedensity of the rigid plastics foam it is possible to change itsrigidifying action. A more dense rigid foam is more rigid than a lessdense rigid foam, assuming that otherwise both have the samecomposition.

In one of the embodiments of this invention the outer shell and inner'rigidifier jointly form a second cavity and a reinforcing spine may beapplied as a third component in the entirety or in part of the secondcavity. Such a spine assists the rigidifying action of the inner layerand toughens the composite article of manufacture. 'In this applicationthe expression ancillary reinforcing element is preferred to theexpression spine.

As stated above, the cellular plastics of this invention may be of opencell or closed cell structure. Most rigid foams are closed cellstructures. Open cell rigid foam structures can be prepared fromurea-formaldehyde and phenol-formaldehyde foaming compositions. Rigidpolyurethane foams with open cell structures can be prepared by the useof special silicone surfactants as additives, designed for thisparticular purpose.

When considering the improvement which the composite articles ofmanufacture of this invention show, versus either the properties of theshell component or of the rigidifier component, utility for manypurposes becomes apparent. In case of a lamp base resistance todeformation is achieved. Such deformation may be caused by compressiveforces resulting from the assembly of the lamp. The resistance to impactalso increases. The thermal deformation is also decreased. The lattereffect is important in manufacturing planters. These have to withstandwarm climate and Subtropical or tropical temperatures withoutdeformation. In preparing wash basins the resistance to hot and coldwater is improved and achieved. The rigidifier may contribute thermalinsulation in addition to rigidifying the end product. While preventingthe buckling and deformation of the shell component the impactresistance and resistance to chipping of the rigidifier component arealso improved. These properties indicate utility for a great manycomposite articles of manufacture. All the shell components used hereinhave an access opening. In most cases the surface area of the accessopening, when compared with the total external surface area of theshell, is small. In other cases it may be larger. For many productsprepared according to this invention the surface area of the accessopening does not exceed one sixth of the total external surface area ofthe shell component. As an illustration it may be mentioned that ahollow cube having one side open as access opening has an access surfacearea of one sixth of the total surface area of the cube.

THE OUTER SHELL COMPONENT Plastisols illustrate an eminently suitablematerial to form the shell portion of the articles of manufacture ofthis invention. Plastisols are well described in the literature, as e.g.in Modern Plastics 26, 78 (April 1949) by Perrone and Neuwirth. They aredispersions of finely divided polyvinyl resin powders in liquid organicplasticizers. The resins contain predominantly polyvinyl chloride withor without some other polymerized monomer. They are polymerized to adegree where they have very low solubility at roomtemperature.Therefore, instead of dissolving them, the plastisols contain the resinsin a dispersed state; the dispersions are usually of creamy consistencyat room temperature and are always fluid to a certain degree. A greatvariety of plasticizers can be used. Dioctyl phthalate is an example.Dioctyl adipate is another example, which frequently is used inadmixture with dioctyl phthalate. Polyester plasticizers are also wellknown. The plastisols usually contain a stabilizer and may containpigment, if so desired. For convenience and to achieve brevity, a fewpublications may be referred to, which all deal with plastisols, theirformulation and application methods: (a) Geon Resin 121 in PlastisolCompounding, Service Bulletin PR4, revised October 1958, B. F. GoodrichChemical Company, 24 pages. (b) The Vanderbilt News. Vol. 26, N0. 3,June 1960. R. T. Vanderbilt Company, Inc. page 12. (c) Modern PlasticsEncyclopedia issue for 1961, published in September 1960. Vinyl Polymersand Copolymers. Pages 129' to 132. Plastisol Molding, pages 765 to 771.(d) Modern Plastics Encyclopedia, 1955 (issued 1964). Vinyl Polymers andCopolymers, page 271. Plastisol Molding, page 690.

Recently a reactive vinyl plastisol system was introduced on the market.This consists of a mixture of a vinyl dispersion resin and a reactivemonomer. The former is dispersed in the latter. When heat is applied tothis system, also used to cause gelation and fusion, the reactivemonomer polymerizes and produces a more rigid product than previouslyproduced with conventional plastisols. Reactive acrylic monomersillustrate examples of such reactive monomers.

When molding plastisols, the material is heated to a gelling temperatureand a gelled film or layer is formed which is very Weak and cheesy, butwhich does not flow. Further heating is required to fuse the deposit,causing the resin to dissolve in the plasticizer and form a toughhomogeneous resinous mass in which the powdered resin and liquidplasticizer have formed a single uniform phase. The fusion transformsthe cheesy deposit or film to a tough leather-like homogeneous shell.

With regard to temperatures required, these are well known in the art.They vary from composition to composition. They vary with time. Thereare, further, three types of temperatures involed: (1) oven temperature,

(2) mold (die) temperature and (3) temperature of the plastisol.Gelation temperature may be accomplished by heating the oven from 150 to600 F. and usually is between a plastisol temperature of 150 to 300 F.The necessary times vary with the temperature used. Fusion isaccomplished by heating the gelled layer in ovens from about 350 F. toabout 650 F. The achieved plastisol temperature for fusion shouldadvantageously range from about 350 to 450 F. The gelation temperatureand fusion temperature depend on the formulation of the plastisols.Therefore some divergence from the above temperature ranges may occur ifspecial formulations are prepared.

The most useful molding methods for plastisol shells are illustrated by(a) slush molding, also called slush casting and (b) rotational molding,also called rotational casting. The expression casting is used becausethe plastisols are applied in fluid state and for this reason theoperation has similarity to metallurgical casting Seamless dies arepreferred for the intermediate products of this invention. They can bereadily utilized, even when complicated undercuts exists in the dies, asthe shells produced from the plastisols are flexible, elastic and have ashape memory, i.e., they recover from their stretched position, obtainedduring removal, to the original molded shape.

When slush molding or slush casting is used, in the first step an excessof plastisol may be poured into the seamless die. As the plastisolreaches gelation temperature, the layer adjacent to the metal wall ofthe mold gels, i.e., solidifies. The thickness of the gelled wall isdetermined by the duration of time the mold is exposed to thetemperature of gelation. The excess plastisol is then removed by pouringoff the liquid portion. Heating is then continue to complete the fusionand the molded shell is then removed or stripped from the mold. Thereare two methods known in slush molding: (i) One Pour Method, and (ii)Two Pour Method. Both are well known in the art and are applicable tomake the shells of this invention from plastisols.

The rotational molding is another method of casting. The basic departurefrom the slush molding is that, intead of an excess of the liquidplastisol, a premeasured quantity of the fluid is used when charging themold. This eliminates the need for removing any excess. As the moldcontaining the charged fluid plastisol is rotated on the rotationalmolding machine and the mold is heated, gelation of the plastisol occursuniformly on the inner surface of the heated mold. By continuing theheating and or increasing the temperature of the mold, the gelledplastisol fuses. The fusion completes the molding of the shell and thecompleted shell is then stripped and removed from the mold.

Whereas the casting by slush molding or rotational molding is preferredto form the shell from plastisols, other methods known in the art mayalso be followed to achieve the same purpose. Objects made of plastisolsfrequently display the defect known as cold flow. Cold flow may bedefined as the warpage or flow of material caused by its normalenvironmental temperature. Cold flow in plastics is analogous to thewarping of a wax candle in a hot climate, and when a thermoplasticproduct is subjected to compression, tension or flexing, the cold flowcharacteristics become even more accentuated. When a condition oflocalized intensified heat, such as that to which lamp bases are oftensubjected, is imposed upon a stressed article, cold flow warpage becomescritical and often results in making further use of the articleimpossible. The application of a rigidifier in accordance with thepresent invention counteracts the cold flow characteristics of plastisolshells, or at least reduces then to commercially acceptable limits.

Considering the aim of this invention of producing rigid articles theflexible nature of the plastisol shells is a drawback. The applicationof the rigidifier component rectifies this defect.

Polyolefins, such as polyethylene and polypropylene are otherillustrative examples for the production of the shell portion of thisinvention. Polyethylene is made today of varying properties with the lowpressure and high pressure polymerization processes. It is supplied withvarying densities, molecular weights, flexibility and othercharacteristics. The types of polyethylene most suitable for thisinvention are pliable, flexible and show some degree of elasticity.Polyethylene is preferred in this invention over polypropylene since itis more easily formed into pliable and flexible shells. Polyethylenecopolymers, such as ethylene-vinyl acetate and ethylene-ethyl acrylatecopolymers, offer improved flexibility and resilience. They arerubber-like and similar to elastomeric plastics. For the production ofshells from polyethylene and polypropylene seamless dies are notsatisfactory and twopiece dies are preferred, using blow molding orother methods. Polyallomers belong to this class of materials, as theyare copolymers of ethylene and propylene.

The shell portion of the articles of manufacture of this invention maybe formed of other materials such as vulcanized natural rubber orsynthetic rubber. The shells may be formed according to known proceduresof rubber technology. One of the methods useful in preparing shells fromrubber is to use latex molding (latex casting) compounds, utilizingplaster of paris molds. The Vanderbilt News, Vol. 27, No. 4, December1961, page 72, deals with latex compounding which can be used to makeshells for articles according to the present invention.

Other suitable plastics materials, which can form the outer layer shellsof this invention are illustrated by methyl methacrylate polymer, ethylcellulose, polycarbonates, polyurethane elastomers, flexible epoxycompounds, flexible polyesters, amongst others. Some illustrativeexamples are given below:

Example A.Methyl methacrylate All percentages in this example and inthis specification are weight percentages. A mixture was prepared of62.5% methyl methacrylate monomer, 0.6% benzoyl peroxide, 2.1% whitecolor paste concentrate, compatible with methyl methacrylate, 34.3%polymethylmethacrylate, DuPonts Lucite 30, 0.5% dimethyl-p-toluidine,totaling The shells were prepared by casting into suitable molds. Thecomposition of this example polymerizes at room temperature. Heating to100-l20 F. accelerates polymerization considerably. Latex molds can beused. Plaster and clay molds may also be used, if coated with gelatin,cellulose acetate, sodium silicate or tin foil. Casting was carried outin a latex mold in 3 subsequent coats and yielded a molded shell withacceptable flexibility and adequate mold surface reproduction.Plasticizers may be incorporated, if desired. Harflex 340 of HarchemDivision, Wallace & Tiernan, Inc. is a suitable resinous-type, primary,non-migrating, saturated polyester plasticizer, compatible with methylmethacrylate monomer. The color paste was used to stain the shell. Itsuse is optional.

Example B.Polycarbonate Polycarbonates can be cast from organic solventsolutions. Polycarbonates dissolve, with ease e.g. in methylenechloride. A solution was prepared from Lexan No. (General Electric Co.)powder to form a solution of 83.3% polycarbonate in 16.7% methylenechloride, yielding 100% of the solution. As an example, this solutioncan be slush cast in latex molds, and air can be blown in to assist involatilizing the solvent. The latex molds are standard in castingplaster of paris objects. The polycarbonate shell remains in the mold.It is very strong, flexible and durable, and can easily be stripped fromthe mold. To reduce the eflect of shrinkage, fillers may beincorporated. A ratio of equal weights of filler 7 to polycarbonate isan illustrative example. The resulting shell is still strong.Polycarbonate resins are marketed by General Electric under the tradename of Lexan. Polycarbonates can be described as polymeric combinationsof bi-functional phenols or bisphenols, linked together through acarbonate linkage. They can also be blow molded and vacuum formed.

Example C.-Plexible epoxy resin The proper composition has at leastthree ingredients. (1) a low molecular weight epoxy resin of theepichlorhydrin-bisphenol A-condensation product type, like ShellChemicals Epon 828. (Epon is a registered trademark of Shell); (2) lowviscosity liquid aliphatic polyepoxides, like Epon Resin 871, whichimparts increased flexibility to Epon resin compositions; and (3) acuring agent, illustrated by diethylenetriamine andtriethylenetetramine, respectively known as DTA and TETA. Othercomparative items, known in the trade, may be replaced for thecommercial products mentioned. Fillers may be present as additionalingredients. A suitable additive to regulate viscosity is asubmicroscopic pyrogenic silica prepared in a hot gaseous environment,marketed by Cabot Corporation under the trade name of Cab-O-Sil. Asatisfactory composition to obtain shells is 44.25% Epon Resin 828,44.25% Epon Resin 871, 2.65% of Cab-O-Sil and 8.85% diethylenetriarnine,totaling 100%. This composition sets at room temperature in about 5hours and at 80 C. it sets in 2 hours. The composition may be variedaccording to principles known in the art. Shells can be molded in latexmolds or other elastomer molds. These are actually multi-pieced plasterof paris molds externally reinforcing an entirely separate secondflexible elastomer mold, having one opening for pouring in thecomposition to be molded and set. The rubber surface is coated with aparting agent and the epoxy composition is slush cast into the molds.The slit mold here described is used to mold shells showing undercuts.Other molds and molding methods can also be used, depending on thearticle to be manufactured. Epoxy plasticizers include epoxy compoundsof fatty oils and their acids. Epoxy novolack resins and cycloaliphaticepoxies are other illustrative members of this group. Polyamids and acidanhydrides may also be used as curing agents.

Example D.Flexible polyesters Polyester resins are usually made in twosteps. In the first step a condensation reaction is carried out betweena dibasic acid and a diol and this is then blended with a monomer.Maleic anhydride and fumaric acid are examples of the dibasic acids.Other unsaturated acids could also be used, like itaconic. Phthalicanhydride and isophthalic acid may be part components of the acids, tosecure desired modifications. The useful glycols form a long list knownin the art. Propylene glycol, ethylene glycol, diethylene glycol anddipropylene glycol are illustrative examples. Neopentyl glycol isanother example. Styrene is most frequently used as the crosslinkingmonomer. Vinyl toluene is another example. Laminac Polyester ResinEPX-l263 is a flexible polyester resin containing styrene monomer.Laminac is a registered trademark of American Cyanarnid. A compositionwas prepared from Laminac Polyester Resin EPX126-3 92.6%, MEK peroxide2.7%, Cobalt Naphthenate solution (6% Co) 0.27%, Laminac Additive #10,1.73% and Cab- O-Sil 2.7%, totaling 100%. MEK peroxide is methylethylketone peroxide. Laminac Additive #10 is a petroleum Wax compositiondispersed in styrene, for ease of incorporation into polyesters. Itimproves surface characteristics. The peroxide is the crosslinking agentand the co balt assists the crosslinking. Flexible polyesters usuallycontain long chain acids or glycols. The gel time at room temperature isabout 10 minutes for this composition. The Cab-O-Sil assists inregulating the thickness of the deposit if slush casting is used formolding. Two or three coats can be slushed to obtain a desired shellthickness. The shell formation occurs at room temperature. More rigidpolyesters can be blended with the flexible one used in this example, tovary properties. Latex molds and those utilized for epoxy resins, may beused with polyesters.

Example E.-Isocyanate elastomers (urethane elastorners) Liquid urethanepolymers, such as DuPonts Adiprene L-lOO, can be transformed into tough,rubbery solids by reaction of the isocyanate group with polyamine orpolyol compounds. In addition, some materials which do not containactive hydrogens, such as the titan'ateesters, appear to catalyzecross-linking. Adiprene 1-100 can be cured with diamines, or moisture(water), or polyols, or by catalysts, such as lead or cobaltnaphthenate, potassium acetate and titanate esters. Tetrabutyltitanateis an example of the esters. One of the popular polyamines is MOCA,which is 4,4'-methylene-bis(Z-chloroaniline). A formula tion isillustrated by parts of Adiprene L-l00 and 12.5 parts of MOCA, whichgives a MOCA percent-equivalent of 95. Parts are by weight. Conditionswere: Mixing temperature: 212 'F., cure temperature: 212 -F., curingtime: 3 hours. LD420 is a different type of liquid urethane elastomer,which yields high quality vulcanizates when cured with MOCA. Arespective formulation is illustrated by 100 weight parts of LD-420(DuPont) and 8.8 weight parts of MOCA. This is mixed and cured the sameWay as Adiprene L-lOO, for the same length of time. It is improved byaftercuring 1 Week at 75 F. at 60% relative humidity. In making a shellrotational molding is recommended both for Adiprene L100 and for LD-420. A silicone mold release is advantageously used to assist separationfrom the molds.

Example F.Ethyl cellulose Ethylcellulose shells can be molded by vacuumforming and injection molding, amongst other methods. The same appliesto cellulose acetate and cellulose acetobutyrate. Combination of castingand hot melt methods may also be used.

The preset molded outer shell components can be prepared by variousmolding proceses. The selected process depends on the selected plasticmaterial and on the shape and size of the shell to be molded. Forillustrative purposes a few examples are given. Casting such as slushcastinlg or rotational casting: plastisol, flexible polyester, flexibleepoxy resin,s methyl methacrylate, polycarbonates from solution, rubberfrom latex, etc. Injection molding or extrusion: plastisol,polycarbonates, ethyl cellulose, polyethylene, cellulose acetate,cellulose acetobutyrate, etc. Vacuum forming: polyethylene,polycarbonates, polyallomers, etc. Blow molding: polycarbonates,polyethylene, polyallomers, ethyl cellulose, cellulose acetate, etc. Hot

- melt process: ethyl cellulose, plastisol or other plasticizedpolyvinyl chloride composition, polyethylene, etc.

Whether a one-piece, two-piece or 'multi-piece mold is required, dependson the selected shell material and, to some extent on the shape of themanufactured article. The molding process also influences the moldselection. Plastisol illustrates a shell forming material which permitsthe use of one-piece molds even if the shell has many undercuts in itsshape.

Methyl methacrylate illustrates a material which requires at leasttwo-piece molds in many instances. Blow molding and vacuum forming areusually carried out in two-piece or multi-piece molds. One-piece moldsform seamless molded shapes. Two-piece molds cause, in most cases, someseam formation. It may be necessary to eliminate these seams. Therefore,seamless molding is of advantage.

The expression that the shell materials are flexible, pliable andresilient is meant in a relative manner in comparison with the innerrigidifier component of the articles of manufacture, i.e. the fleshportions which are relatively rigid. The composite article itself isrigid and resists indentation, chipping, etc. The flesh portionrigidifies the flexible shells and improves resistance to cold flow orheat distortion. The shell materials protect the rigidifiers fleshportion from fracture and improve their resistance to impact. Thismutual improving effect between shell and flesh materials is unexpectedand surprising and the effect obtained could be described assynergistic.

From the shell materials discussed above, polyethylene andpolycarbonates, when blow molded, are used at a limited thickness. Inusing the various shell materials with the rigid foam inner rigidifiercomponent of this invention, the composite article manufactured showselimination of flexibility, improved resistance to impact and in manycases the tensile strength of the composite article shows improvementwhen compared separately with that of the shell or flesh material. Theseobservations apply to shells made of plastisols, flexible polyesters,flexible epoxy resins, polyethylene, polypropylene, polyallomers, polyurethane eastomers, rubber, polycarbonate, ethyl cellulose, methylmethacrylate, amongst others. The degree of the above discussedimprovements may vary according to the selection of the shell formingmaterial, its secondary compounding ingredients, thickness and shape ofthe shell, formulation of the flesh material and its thickness, amongstother factors.

According to a more recent type of moldin method shells can be molded byrotational casting of powders. Polyethylene in powder form illustratessuitability for this method. The powder is rotated to obtain uniformdistribution over the interior surface of the mold. The mold is thenheated to obtain the required molding temperature.

For the purpose of forming the outer shell component the thermoplasticplastics materials are preferred. These are illustrated by plastisolsand polyethylene. For the purpose to form the inner rigidifier componentthe thermosetting rigid foams are preferred. The reactive vinylplastisol systems containing reactive acrylic monomers, discussedfurther above, are considered as thermoplastic for the purposes of thisinvention and are included in the preferred group of plastics for thepurpose of forming the outer shell component.

THE INNER RIGIDIFIER COMPON-ENT As described earlier, the flesh portionof the products of this invention is the inner rigidifier componentwhich in turn is snugly attached to the outer shell component and is inintimate contact therewith. The inner rigidifier component comprises arigid foam. One of the purposes of the application of the innerrigidifier component is to rigidify the outer shell component. Therigidifying action is of particular importance, where the outer shellcomponent is flexible, according to a favored embodiment of thisinvention. A further object of the inner rigidifier component is toreinforce the outer shell component and in many cases to provide bodyand structural stability to the composite article of manufacture.

Rigid plastics foams are well known in the art and are discussed e.g. byT. H. Ferrigno in Rigid Plastics Foams, Reinhold Publishing Corp., 1963.They are illustrated by rigid polyurethane foams, polystyrene foams,epoxy foams, polyvinyl chloride foams, phenolic resin foams, siliconefoams, syntactic foams, cellulose acetate foams, acrylic foams,polyester foams, asphalt foams, amongst others. These rigid plasticsfoams are not equally suitable for the instant invention. For thisreason they will be discussed individually. The favored foam systems areillustrated by the rigid polyurethane foams. They will be discussed atsome length.

(1) Rigid polyurethane foams Diisocyanate based polyurethane foams aredescribed amongst others in German Plastics Practice by DeBell 10 etal., 1946, PP. 310, 316 and 455 to 465. Some of the problems encounteredin this field of the art are discussed by H. L. Heiss et al., Ind. Eng.Chem., 1954, pp. 1498 to 1503.

In the preparation of polyurethane foams several com ponents are used.Some of the components permit the use of alternatives. One of thenecessary components is a compound containing free isocyanate (NCO)radicals. This component can be a polyisocyanate, usually adiisocyanate, or a reaction product thereof, containing free NCOradicals. Such reaction product is sometimes called an adduct or aprepolymer or a quasi-prepolymer, and is usually formed with a polyol.The second necessary component supplies active hydrogen atoms, suppliedby free hydroxyl groups derived from a polyol or from ahydroxyl-terminated polyester. The free hydroxyl groups are reactive.Alternatively polyesters or compounds containing reactive amine or COOHgroups can supply the active hydrogen contributing second component.When free hydroxyl groups or free carboxyl groups are reacted with freeisocyanate radicals, CO gas is formed in situ in the reaction which inturn acts as the foam forming gas. These types of foam are also known ascarbon dioxide blown foams. In many cases small quantities of water arealso added to the reaction mixture in order to react with the free -NCOgroups, forming again CO in situ. Ureas are frequently formed asintermediates, which react in turn with additional free NCO groups toyield urethanes or cause crosslinking of the polymers formed in thereaction. In many formulations catalysts are also present and optionallyauxiliary foamers or blowing agents may be added, liketrichlorofluoromethane.

Aryl diisocyanates are preferred, but alkyl diisocyanates may also beused. The most popular diisocyanates are the toluene diisocyanates, alsocalled tolylene diisocyanates. 2,4 tolylene diisocyanate and 2,6tolylene diisocyanate are frequently used inadmixture with each otherand commercially available products include mixtures of these twoisomers in proportions of 60%40%, 65%35%, %20%. The 2,4 tolylenediisocyanate is also produced in 99%100% purity, and is also called TDI.The 80/20 and 65/35 mixtures are called TDI-mixture, with the respectivepercentage identification added. Other diisocyanates are 3,3-bitolylene4,4'-diisocyanate (TODI); diphenylmethane 4,4'-diisocyanate (MDI);(p,p-diphenylmethane diisocyanate); polymethylene polyphenylisocyanate(PAPI, essentially a tri-functional polyisocyanate);1-chlorophenyl-2,4-diisocyanate; diphenyl-4-6-4'- triisocyanate; 1,6hexamethylenediisocyanate; p-dixylyl methane 4,4 diisocyanate,di-(p-isocyanylcyclohexyl) methane; tri- (p-isocyanylphenyl)methane.

The principal commercially available polyhydroxy compounds are ethyleneoxide and propylene oxide adducts of polyfunctional active hydrogencompounds such as glycerine, sorbitol, trimethylolpropane, ethylenediarnine, sucrose, etc. These compounds are polyethers, but .SIHCC theyare primarily polyols, the term polyether polyol is properly used. Rigidfoams require the use of highly functional reactants. These are mostuseful when based upon polyalcohols having functionalities of at least 3and in many cases greater than 3. The fluidity of these reactants atambient temperatures is important as most of the time the reaction iscarried out at room temperature and in absence of diluents. AtlasChemical Industries offers propylene oxide condensates of sorbitol.Union Carbide Chemicals Co. offers amongst others, diethylenetriamine-alkylene oxide condensates, triols, hexols, pentols and otherpolyols. Wyandotte Chemical Corp. markets a variety of polyetherpolyols, which are propylene oxide or ethylene oxide derivatives basedon trimethylol-propane or on glycerol, or on pentaerythritol, or onsorbitol. In one type of polyether polyols marketed by Dow Chemical Co.,sucrose is reacted with propylene oxide, yielding cyclic polyfunctionalpolyether polyols. Olin-Mathieson Chemical Corp. offers0,0'-bis(diethanolaminomethyl)- p-nonylphenol. 1,2,6-hexanetrio1 isanother example of usable polyols.

Various hydroxyl, carboxyl and amide bearing compounds may be reactedwith polyisocyanates to form rigid foams. Pittsburgh Plate Glass Companymarkets Selectrofoam Resin 6002, which is a high viscosity saturatedpolyester resin, compatible with toluene diisocyanate. In spite of itshigh viscosity, it exhibits fair mixing properties in batch-typeprocesses. It has a Hydroxyl Number of 440. Products have been preparedprimarily for flame-proofing purposes which can replace part of thepolyether polyol in the reaction. They are propylene oxide condensationproducts of aryl or alkyl phosphonates, like di-polyoxypropylenephenylphosphonate and di-polyoxypropylene chloromethylphosphonate Analkyd, con- 7 taining free carboxyl groups and reactive withdiisocyanates, was prepared in Germany according to DeBell, from 2 /2mols of adipic acid, /2 mol phthalic anhydride and 4 mols oftrimethylolpropane, having an acid number of 35 and containing residualwater.

As the handling of diisocyanates requires special and skilled care andprecautionary measures it became useful to pre-react the diisocyanatcsprior to foaming and to complete the reaction in a subsequent step. Whenpolyesters and less eflective catalysts are used in the reaction, it isadvantageous to prepare prepolymers. In this case the polymerizationreaction is partially completed prior to foaming, and therefore lessheat of reaction is generated during the foaming step than in theone-shot method. This is advantageous in high density foam preparation,like 6 p.c.f. (pounds per cubic foot) or higher, In preparing theprepolymer a polyester of known hydroxyl number is charged into ajacketed, agitator-equipped, glass lined or stainless steel reactionkettle which has been flushed free of moisture by dry air or drynitrogen. The following is an illustration of proportions:

1) 91.7 parts by Wt. of TDI with combining weight of 87.4 excess), (2)87.5 parts by weight of polyester with a combined hydroxyl number andacid number of 450 and having a combining weight of 125, and (3) 2.7weight parts of water, having a combining weight of 9. The reactants aremixed at room temperature, the exothermic reaction is permitted todecline and the batch is held at about 100 C. for approximately onehour. It is advantageous to keep the water out from the initial reactionand to prevent entry of airborne moisture. The water is added prior tofoaming in combination with the catalyst-emulsifier mixture. Excess freeisocyanate (NCO) content is usually about 5%, but depends on the amountof Water to be used in the foaming reaction. The prepolymers overcomethe handling of noxious diisocyanate in the foam producing plants. Theyare, however, very viscous, present problems in pumping and requiresmall proportions of addition of catalyst-emulsifier mixture, such as aratio of 2 to 100 parts of prepolymer. This makes the meteringdiflicult.

The introduction of quasi-prepolyme-rs or partial prepolymers representsan advantageous progress in rigid foam technology. They are preferredfor the instant invention. They are particularly advantageous withthermoplastic shell components. The quasi-prepolymers are usuallyprepared by reacting of about 4 to 4.5 equivalent weights ofdiisocyanate with 1 equivalent weight of polyether polyol. When usingTDI, it is customary to mix all of the diisocyanate with one half of thepolyol earmarked for the reaction and to allow the exothermic reactionto subside and then add the remainder of the polyether polyol. The batchis then adjusted to a temperature of 70 C. and maintained at thattemperature for an hour. Moderate agitation is used during the reactionand dry inert atmosphere is provided. The viscosity of thequasi-prepolymers ranges, in most cases, between about 4000 and about7500 cps., with a tolerance of 1000 cps. for a given grade. If excessTDI is added, the addition may bring the viscosities down to cps. orless. The quasi-prepolymers is reacted with the proper quantity ofadditional polyether polyol just prior to the foaming operation. Theadvantages of using quasi-prepolymers are numerous. Some of these are asfollows: good storage stability of the ultimate reactants; reduction ofthe exothermic reaction; reduction of the noxious property of TDI andthe ability to produce uniform foams with primitive mixing equipment.

*Quasi-prepolymers may be formulated into delayed action one-partsystems by partial blocking of the prepolymer with tertiary-butylalcohol. Boric acid, surfactant and catalyst are added. Such blockedcompositions are stable at room temperature and produce rigid foams whenheated to elevated temperatures, such as C.

The rigid foam forming compositions may contain other ingredients inaddition to the diisocyanate component and the component reactivetherewith. Catalysts, surface-active agents and additional blowingagents are illustrative of such other additives.

The catalysts promote the reaction, shorten reaction time and channelthe reaction towards the proper and desired end product. Examples ofN-containin'g catalysts are N-methylmorpholine, N-ethylmorpholine,triethylenediamine, diethylethanolamine, dimethylethanolamine,triethylamine and N,N,N',N'-tetramethyl-1,3-butanediamine. The aminesare active at pH ranges of 10 and higher. Metallic catalysts areillustrated by stannous chloride, stannous octoate, ferricacetylacetonate, tri-n-butyltin acetonate, bis(2-ethylhexyl)tin oxide,di-n-butyltin diacetate, di-n-butyltin dilaurate, dimethyltindichloride. Synergistic effects are obtained by using certain organo-tincompounds with tertiary amines. For instance the mixture of 1mol-percent triethylamine combined with 0.001 mol percent of di-nbutyltin diacetate have a greater relative activity than either onealone, used in the same mol-percent ratio. In general it may be stated,that rigid foams require lower concentrations of catalysts than doflexible foams.

When water is added to polyester prepolymers to provide carbon dioxideblowing, difficulties are encountered, as water is not readilydispersible in such systems. Various nonionic and anionic surface-activeagents are found effective to act as emulsifying and wetting agents.With polyether polyols the viseosities are lower, still surfaceactiveagents are useful to provide uniform foam cell structure in rigid foams.The preferred surface-active agents nowadays are organo-silicone fluids.They are orgauo-silicone block copolymers. Dimethyl-silicone oil is onedesignation. These silicone compounds are soluble in Water,polyisocyanates, quasi-prepolymers, trichlorofluoromethane and amines,and are dispersible in polyether polyols and organo-tin catalysts. DowCorning 113 is a silicone-glycol copolymer, specifically developed forrigid polyurethane foams. General Electrics SF-l034 and XF- 1066 arecopolymers of dimethyl polysiloxane and polyalkylene ether. They havesurface-active properties. Silicone surfactants are usually used inproportions of 0.5% to 1% of the total weight of the foam ingredients.In some cases the proportion may be lowered to 0.25 The siliconespromotes bubble formation, equalize surf-ace tension on the surface ofthe bubble, impart resilience to the film and promote resistance tocollapse when distorted during the rising of the foam.

Halocarbons are used as additional blowing agents. The same types can beused as in refrigeration: CCI F, CCl F and CCl F-CClF For the purposesof this invention trichlorofluoromethane is most advantageous, as itsboiling point and evaporation characteristics are the most suitable forworking close to room temperature. Advantageously halocarbons have lowthermal conductivity and this increases with temperature rise to alesser degree than it does with C0 or air. They have a high degree ofhydrolytic stability and do not dissolve in water. By their lack 13 ofhydroscopicity they reduce the susceptibility of prepolymers orquasi-prepolymers to air-borne moisture. CO blown foams cannot beproduced reliably at low densities. Their practical lower limit is about4 p.c.f. (lb./cu. ft.). For economic reasons the preferred foamdensities in this invention are about 1 /2 to 3 p.c.f. These can beformed with good uniformity by using halocarbon blowing agents.

Flame retardants are another group of additives. Whereas phosphoniumcompounds with reactive OH groups are available to replace part of thepolyether polyol reactant component, the trade frequently usesplasticizer type additives which are non-reactive with NCO groups, toobtain flame retardant properties. Examples are: tris- (2,3dibromopropyl)phosphate and tris-(chloroethyl) phosphate.

For various specific effects other additives may also be present, suchas cellulose derivatives to control bubble formation, and comminutedminerals to assist in reducing shrinkage after foam formation. Hydrousaluminum silicates and kaolinite illustrate the latter group.

Manufacturing methods and problems related to the instant invention willbe discussed further below. These will be illustrated by rigidpolyurethane foams. At this point it is logical to discuss othersuitable rigid plastic foams. Before doing so, a few facts have to bepointed out, to explain the difiierence in degree of applicability ofthese rigid foams to the instant invention.

The shell component of the herein claimed article of manufacture ismolded of a pliable plastics. The pliable plastics are in many casesthermoplastic and may require a mold not only in the step preparing theshell component but also in the foaming step, should elevatedtemperatures be needed either for the foaming step or for theaftercuring of the rigid foam. The use of a mold during the foaming stepis required to prevent deformation of the molded skin, providing theshell is thermoplastic and the foaming step requires elevatedtemperatures. The use of molds during the foaming step presents severalproblems. As the foam solidifies, the mold has to be at least atwo-piece mold in order to permit removal of the article of manufacture.If undercuts are present in the article of manufacture, a multi-piecemold is required or the mold has to be disposable and removable by e.g.fracturing. Such multi-piece molds are expensive. The molds, ifpermanent, are tied up for long periods and prevent mass productiontechniques. The foam-in-place method of foam production is the mostadvantageous for this invention. From these considerations it follows,that if foam production can be carried out in the absence of molds andthe molded skins themselves can be used alone for the foam-in-placemethod, great advantages are derived in producing the articles ofmanufacture of this invention. It also follows that the type of foamwhere higher temperatures are required and expensive molds are involvedis less attractive for this invention.

(2) Polystyrene rigid foams Polystyrene is readily available. Its rigidfoams are less adaptable to the preferred mass production techniques ofthis invention than polyurethane foams. Polystyrene foams cannot beapplied with ease with the foam-in-place methods. They require theapplication of heat. This places limitations on their use. Smaller batchmixing operations cannot be carried out with them either.

The extrusion technique is one method to prepare rigid polystyrenefoams. It injects a volatile liquid, like methyl chloride into thepolymer melt and the melt expands upon release of pressure and coolsrapidly. This method produces a low density product. It is moreadaptable to producing slabs which then can be placed mechanically intothe shells and attached thereto by the aid of adhesives.

In another method styrene is polymerized, containing the foaming agent,in an aqueous emulsion and beads or rounded granules are produced. Thebeads so formed are filtered and washed. Hydrocarbon blowing agents canbe used, such as pentane, hexane or heptane. The blowing agent shouldboil below or at the softening point of the polymer. This can beillustrated by the temperature of 175 F. Diethyl ether and ethanolmixture is also used, by first preparing the granules and then soakingthem in the solvent. Petroleum ether yields less than l p.c.f. foamsusing 68% of the blowing agent. Alkyl phenol polyoxyethylenecondensation products or oil soluble higher alcohols (C to C are usedfor specific purposes. This type is called expandable polystyrene.Preexpansion or pre-foaming is advisable if low density foams are to beproduced. One of the molding methods is the steam chest method. For thepurposes of this invention one can expand polystyrene beads inside themolded shell and adjacent thereto. The shell component is placed in asuitable mold, the polystyrene beads are placed into the shell and heatis applied to accomplish the expansion. An adhesive layer may beadvantageously used in between the shell component and the foam tosecure proper shrinkage relationship between the two components.

Injection molding can be carried out with expandable polystyrenecontaining a halocarbon blowing agent. This is not too applicable to theinstant invention. Blow molding, beginning with an extrusion operationis also a method. 0.2% citric acid monohydrate and 0.25% sodiumbicarbonate is used as microcell generating additives.

When a prefabricated foamed object is bonded to molded shells, drying,setting or hot melt adhesives may be used to accomplish the bonding.

(3) Rigid epoxy foams The commercially available epoxy resins arecondensation products of epichlorhydrin and bisphenol A. They arepolymerized to different molecular weights and range from liquids tohard fragile solids. Epon 828 illustrates a commercial product useful inpreparation of rigid foams from liquid compositions. It has a viscosityof 50 to poises at 25 C. and an epoxide equivalent of to 210. Typicalexamples of highly reactive curing agents are diethylene triamine andtriethylene tetramine. For specific purposes other curing agents may beused, such as (aromatic polyamines, ethoxylated and cyanoetihylatedamines, tertiary amines, cyclic amines, acid anhydrides and amineterminated polyamides, amongst others. Difunctional curing agents wouldbe expected to yield linear polymers with the difunctional epoxy resins.However, tertiary amines promote crosslinking between polyfunctionalamines and epoxy resins. The presence of hydroxyl groups accelerates thereaction. High density foams can be based on Epon 828 and prepared byusing nitrogen releasing organic compounds as blowing agents, anemulsifier, a solvent to reduce the exothermic reaction temperature anda polyamine curing agent. The resin has to be preheated to about 110 C.and this imposes limitation on its use. In low density foams halocarbonblowing agents are used. Silicone surface active agents assist insimplifying and extending the use of epoxy foams. Halocarbon 11(fluorotrichloromethane also called trichlorofluoromethane) yields 2p.c.f. foams with ease.

Foam-in-place systems are available from variou suppliers. They aremarketed as proprietary products. They are supplied as resin and curingagent. The resin component must be kept at 65 F. prior to mixing toprevent loss of the halocarbon blowing agent. Initiation time for startof foam rising is 30 seconds and foaming is completed in 1 to 3 minutes.The foam can be handled in 15 minutes but keeping it in a mold for about2 hours is recommended. Foam spray compositions are also available. Theepoxy foams have excellent adhesion properties to various surfaces withwhich they are in contact while still liquid.

(4) Polyvinyl chloride resin rigid foams Polyvinyl chloride (PVC) resinsand copolymers are popular members of the plastics family. There aredifiiculties in their processing to foams, although their properties aredesirable in rigid foams. There are two grades on the market of interestin rigid foam manufacturing. One of them is a vinyl dispersion resinContaining about of vinyl acetate as part of the copolymer with PVC.This resin is very rigid and plasticizers are used to obtain therequired properties. The other resin is called Type 1, low molecularweight resin and is essentially a low molecular polyvinyl chloride. Thesolvated gas process requires pressures of up to 300 atmospheres andapplication of a pressure vessel. This is not suitable for the instantprocess when low production cost is an aim. The gas releasing agentprocess has better possibilities. Gas evolving blowing agents are used,such as nitrogen compounds. The decomposition temperature is about 100C. Cornpounding on a cold 2-roll rubber mill of the followingcomposition yields a useful product: 100 weight parts of PVC dispersiongrade resin (Geon 12]), 70 weight parts of acetone, weight parts ofdibasic lead phosphite stabilizer, weight parts of Nitrosan, which is a70/30 mixture of N,N-dirnethyl, N,N'-dinitrosoterephthalamide/whitemineral oil. The density of 2 to 2 /2 p.c.f. can be achieved with thiscomposition, The ingredients, less the acetone, are blended and theacetone is then added. The mixture is homogenized by one pass throughthe 2- roll mill. Metal molds heated 10 minutes with 100 p.s.i. steamare used and the molds are cooled. Heating the mixture for l5-20 minutesat 100 C. completes the foam expansion. The shell forming materials haveto be properly selected to Withstand these conditions. providingfoam-in-place process is used. Other solvents can replace the acetone.Other blowing agents are also operative, like azobisisobutyronitrile,azoamides, nitroso compounds, etc. Crosslinked plasticizer modified PVCfoams are produced by the aid of epoxidized oil (soya) as theplasticizer, which crosslinks upon heating. In this system pyromelliticdianhydride is recommended as the curing agent. This type of foamrequires curing temperatures up to 163 0, (374 R), which excludes itfrom many of the uses herein contemplated.

(5) Phenolic resin rigid foams Phenolic foams are made from casting typephenolic resins containing between 1.2 and 3.0 mols of formaldehyde permol of phenol. For foaming agents carbonate salts are used, such assodium, potassium, ammonium, calcium, magnesium and other carbonates.The intermediate casting resins are commonly called resoles. Many of thecarbonates have to be added just prior to foaming. Others may beincorporated into the resin, providing it is neutralized to a pH of 7 orhigher. Acid catalyst is then used. which promotes the evolution ofcarbon dioxide. Metal powders may be used to generate hydrogen gas asthe blowing agent. This presents the need for safety precautions.Organic gas generating agents are controlled with greater ease. Examplesare: p,p'-oxybis(benzenesulfonylhydrazide), dinitrosopentamethylenetetramine and diazonium salts, such as benzene diazoniumsulfate. Air has also been utilized as well as other agents, likehydrogen sulfide, halogenated hydrocarbons, etc. The acid curing resinfoam is dried and cured after being foamed by the gas. Surface activeagents are added to secure uniform cell structure. Alkyl aryl sulfatesand sulfonates, alkylene oxide-phenol condensation products and lecithinare examples. The phenolic foams are usually brittle at low foamdensities. With many types post curing is required, e.g., for 8 to 10hours at 140 to 200 F. They can be foamed-in-place. They are lessadaptable for the purposes of this invention than the rigid polyurethanefoams, but with proper care of formulation and processing method, theycan be used.

16 (6) Urea-formaldehyde rigid foams Various methods have been used toproduce ureaformaldehyde resin foams. The liquid resin is filled withair or gas under agitation, while in water solution, with surfactantsand acid catalysts present. Gas can also be dissolved under pressure inthe liquid resin. In one recent development low boiling liquids areemulsified in the liquid resin. The resin contains dibutyl phenyl-phenolsodium disulfonate as the emulsifier. Halocarbons or propane areemulsified into the solution under pressure at low temperatures. Uponaddition of a catalyst, like phosphoric acid, the exothermic reactionvolatilizes the emulsified liquid and causes foam formation. This typeof foam is closed celled, whereas other foaming systems cause formationof open cells. The liquid blowing agents are used in proportions of 2 to30% based upon the Weight of the resin solids. Polyethylene glycols areadded to increase the toughness of these otherwise brittle foams. Whenproperly plasticized, these foams make useful products for the purposesof this invention. Low temperature curing resin formulations arepreferred.

(7) Rigid silicone foams The polymers forming the silicone foams aresilicone oxygen compounds, like siloxanes. They are in the moreexpensive range and are used where good electrical insulatingproperties, low Water absorption, good thermal stability are required.The polyorganosiloxanes can be powders or liquid. Foaming-in-placerequires surface treatment of the cavity of the skins to secureadhesion. The foams can be coated with silicone elastomers for maximumtemperature resistance. High temperatures are required to produce andset these foams, all equal to or above 300 F. and this reduces theirusefulness in many of the applications herein contemplated. As hydrogenevolves in many cases, precautions for safety of the operation arerequired.

(8) Polyester rigid foams It is difiicult to foam polyesters by currenttechniques. The start of polymerization causes a stifi gel to form,which is not readily expanded by foaming agents. The polyesters arethermosetting partial polymers having high molecular weights comparedwith urethane prepolymers and epoxy resins. Even if the degree ofpolymerization is as low as 5%, the gel is non-thermoplastic and rigidand will not deform as the blowing agent vaporizes or releases gas.Polyesters containing residual hydroxy and carboxyl end groups reactwith diisocyanates and such hybrid polymers can be foamed by carbondioxide evolution or by the incorporation of halocarbons. Surfactants,water and peroxides are present frequently in such foaming operations.Ways and means are being developed to foam polyesters. One method e.g.,is using methacrylic acid polyesters exposed to ionizing radiation.Decomposition and polymerization set in simultaneously causing thepolyester to foam.

(9) Miscellaneous rigid foams Cellulose acetate foams were used inaircraft manufacture. The extrusion process is used utilizing a mixedliquid non-solvent (mixing of acetone and ethyl alcohol) at roomtemperature as the blowing agent and comminuted mineral of to 325 meshparticle size as the nucleating agent. The solvent mixture dissolvescellulose acetate at a temperature exceeding F. During the hot extrusionthe solvent plasticizes and simultaneously foams the resin. Whereas withthis method boards and rods can easily be manufactured, it is quitedifiicult to adapt cellulose acetate foams for the purposes of thisinvention.

Rigid acrylic foams are suitable for coarse celled applications, wheremaximum resistance to degradation by ultraviolet radiation is required.Alpha-chloroacrylic acid ester polymers may be polymerized at roomtemperature.

The polymer decomposes upon heating to 150 to 180 C., to yield analkyl-chloride foaming agent. The internally generated foaming agentproduces foams of about 3 p.f.c. The inclusion of dimethyl siloxanepolymer surfactant for cell size control and addition of alcohol orparaffin oil to the monomer prior to polymerization provides finer celldiameters.

Asphalt foams can be prepared by releasing gases under pressure intothis thermoplastic material in a manner similar to other foamedthermoplastics. In another method sodium bicarbonate is used as theblowing agent and aluminum stearate as a surfactant. By controlling theasphalt temperature carefully the gas release is obtained at a uniformrate and the gas is effectively entrapped. Special apparatus isavailable to heat the high melting asphalt and to inject gas or ablowing agent. The use of cold flow retarding agents is advantageous,like fillers, asbestos, gelation agents and high melting resins.

Ebonite, which is hard rubber containing 30 to 40% sulfur can beexpanded by foaming. Plastics, having high softening points require highpressure equipment to contain the blowing agent and the polymer mixtureexpands upon sudden release of pressure. Polypropylene, polyamides andpolycarbonates can be foamed with variations of this method.

A special class of rigid foam is called syntactic foams. These dependfor foam formation on hollow microspheres or microballoons, and not onthe resin used for bonding. Two types of microballoons are available.One is based upon a phenolic resin and the other one upon silica. Thephenolic spheres have an average particle size diameter of 0.0017 inchesad a particle size diameter range of 0.0002 to 0.005 inches. Bulkdensity is 3 to 5 p.c.f. true sphere density of 12 p.c.f. The spheresare filled with inert gas, such as nitrogen. Glass microballoons arebeing made under a license of Standard Oil Co. (Ohio). Microballoons areeasily incorporated into liquid thermosetting plastics, like epoxies orpolyesters. They form trowellable mixes and can be placed by and to formsandwich structures. Room temperature curing polyesters and elastomersillustrate suitable binders. Densities of syntactic foams are not as lowas with foamed-in-place systems, as high density resin fills theinterstices. 20 to 25 p.c.f. are illustrative densities. In the instantprocess they could be used where the rigidifier foam is applied as acomparatively thin layer and does not fill the cavity of the moldedshell fully. This limitation is primarily imposed by consideration ofeconomy.

SELECTION OF THE INNER RIGIDIFIER COMPONENT In selecting the rigidplastics foams, one has to consider the problems relating to thepreparation of the articles of manufacture of this invention. The outershell component is formed in a mold. During the foam producing operationin some cases the shell may be left in the originaLmold in which it wasprepared. In other cases the shell is removed from the mold prior to thefoam producing operation and the foam formation is carried out either ina second mold or without the aid of any mold, using the shell itselfalone in shaping the inner rigidifier foam component. The setting of therigid foam rigidities the composite article of manufacture, and in orderto remove it from the mold after the foam has solidified, providing amold is used during this step, a multi-piece mold is required. Suchmolds are difiicult to operate and require precision tooling. Thereforeit is of great advantage if the inner rigidifier rigid plastics foamcomponent can be prepared in the absence of any mold, using the shellcomponent alone to shape it during its formation.

I A further problem arises when the preparation of the foam or itsapplication requires temperatures at which the shell component maydeform. Additional problems relate to the shrinkage of the rigid foaminner rigidifier after the foaming has been completed. It is ofadvantage if the outer surface of the inner rigidifier foam componentremains in steady contact with the inner surface of the outer shellcomponent during and after preparation of the end product. This requirescontrolled shrinkage properties. 4

Foams having no predetermined confinement are known as free rise foams.The volume expansion of free rise foams is limited only by thethermodynamics and reaction rate of the system. In producing foams inthe interior of shells, as they are produced in'the instant invention,the foam is always confined at least by the interior surface of theshell. In the instances where the cavity of the shell is fully filled bythe foam, the foam is fully confined with the exception of the accessopening (filling hole). In other instances an interior core or formassists in the confinement. In still other cases the foam is confined bythe interior of the shell on at least one surface and freely rises tofill the interior cavity. Any excess may force itself out of the accessopening. In the cases of foam confinement, distention and distortion ofpliable shells can result and, as a consequence, a reinforcing mold overthe shell may be required during the foaming operation. Free rise on theinterior surface does not extend a distending pressure on the shell.Thus, a reinforcing mold over the pliable shell is not necessary duringthe foaming operation. It can be seen that the absence of need for asecond mold during the foaming operation is of great advantage. In caseswhere the foam is otherwise totally confined, it can be noted that afterplacement of the foaming composition the filling hole can be blocked tobring about a mild back-pressure that can assist in forcing theexpanding foam to fill the interior spaces and undercuts.

To avoid excessive shrinkage of the inner rigidifier component during orafter its preparation is of importance for the sucess of the productsprepared hereunder. Quasiprepolymer and prepolymer rigid polyurethanefoam compositions are preferred, as they can be formulated with greaterease to produce low shrinkage. However, more recently, one-shot typerigid polyurethane formulations have also been formulated with lowshrinkage properties. It has been found, that efiicient but slow mixingof the foaming components reduces shrinkage. This can be achieved by theso called folding action mixing, using an up and down and front to backmotion, used for paint mixing. Machines are available to perform suchmixing with efiiciency and within the required short periods before foamrise starts.

Based on some of the above considerations, rigid polyurethane foams areeminently suitable for the purposes of this invention. They permit aroom temperature initiated reaction. Means are available to reduce theheat of the exothermic reaction. The quasi-prepolymer systems permituniformity of foam structure and require only primitive mixingequipment. Compositions suitable for foamin-place type application arealso available today from epoxy resin rigid foams. They are alsosuitable for spray application if properly compounded. Preheating of thecompositions to to C. is required.

Polyvinyl chloride type rigid foams can be prepared by various methods.The gas releasing agent process can be carried out at temperaturesaround 100 C. and molds can be heated by steam of 100 p.s.i. pressure.Foam-inplace method is applicable and even rotational casting or slushcasting is possible. Gelling and fusing the rigid foam requirestemperatures which in turn require molds to prevent the deformation ofthe skin portion. Phenolic resin rigid foams can be prepared at roomtemperature and foam-in-place method is applicable. After-cure at 200 F.is advantageous and sometimes required. They are brittle by nature andmay require plasticization. The ureaformaldehyde resin rigid foams canbe prepared at room temperature and are also brittle, but can beplasticized. Polystyrene can be used from expandable beads. However,heat is required in the nature of to 200 F. The beads are preheated to atemperature above the softening point of the polymer. Pro-expansion isadvantageous and heat is applied for completing the foaming and fusingthe outside walls of the beads together. Polystyrene is difficult toapply by the foam-in-place method. Silicone foams require 300 F.temperatures or more. Low density polyethylene can form foams of lowdensities, such as 2 p.c.f., illustrated by Ethafoam of Dow Chemical. Itrequires elevated temperatures in manufacturing and it is hard to use bythe foam-in-place method. More recently roomtemperature curing siliconefoams have been formulated of two liquid components. They are blendedand poured in place. The reaction is slightly exothermic buttemperatures rarely exceed 150 F. It requires 10 hours or more forcompletion of the process. The list herein discussed is not a completeevaluation of all plastics rigid foams and their comparative values anddisadvantages, but merely an illustration of how to evaluate forsuitability.

The most preferred rigid plastics foam formers for the purpose of thisinvention are the rigid polyurethane foam compositions. The nextpreferred foam formers are the rigid epoxy resin foam compositions. Thermosetting foams are preferred over thermoplastic foams. Low curingtemperatures and fast foam setting rates are of advantage. The settingrate should not be so fast as to prevent adequate distribution of thefoaming composition throughout the inner surface of the outer shellcomponent.

PREPARATION AND APPLICATION OF RIGID PLASTICS FOAMS The preparation andapplication of rigid foams according to this invention will beillustrated with rigid polyurethane foams. In one of the methods batchtype equipment is used. Simple pails and sticks or propeller typeagitators are used frequently to mix the required ingredients where lowvolume pours are required. In such cases quasi-prepolymer formulationsare preferred as they permit proper control of the rise time. In thismethod formulations are used which delay the reaction to start notearlier than one half minute after the ingredients are mixed. Thetemperature of the prepolymer is usually between 70 and 100 F. Thepolyether polyol component is usually maintained at about 65 to 68 F. toprevent loss of the halocarbon blowing agent whose boiling point isaround 75 F. The loss of blowing agent would result in higher densityfoams. The preferred p.c.f. does not exceed 3. In some cases foams withp.c.f. of up to 25 are useful. The ingredients are weighed out orproportioned by volume in separate clean containers. The cooledpolyether polyol is added to the prepolymer. Mixing is completed inabout 15 seconds. Mixing with turbine or disc type mixing blades atabout 1000 rpm. for 15 to 25 seconds is illustrative. The mix isimmediately poured after mixing and prior to the start of the foaming.The type of compounds supplied for batch mixing of two component systemsrise to full height in 3 to 5 minutes. Most formulations are designed toprovide a free rise of about 12 inches. Higher halocarbon concentrationsare used for preparing thick sections.

Quashprepolymer two-package systems are marketed by various supplierswith varying qualities. As illustration the Nopcofoam I-I2N andNopcofoam H-l03N systems are mentioned, supplied by Nopco ChemicalCompany. The components are marked as T-component and R-component. TheT-component is the quasi-prepolymer formed by the diisocyanate and apolyether polyol. It has reactive -NCO groups and supplies theisocyanate radicals for the foaming reaction. The T-component may alsocontain surface active agents, such as the silicones. The R-componentcontains the polyether polyols supplying additional OH-grouping for thefoaming and polyurethane forming reaction. in this H-series theR-component contains the fluorocarbon blowing agent, the catalyst, suchas N-ethyl morpholine and dibutyltin dilaurate and may also contain allor part of the surface active agents, such as the silicones. Thesuitable fluorocarbon is illustrated by Freon #11, which istrichlorofluoromethane, having a boiling point of about 74.7 F. TheH-series of Nopcofoam compounds have a fast curing cycle. Withformulation changes the curing speed and the p.c.f. of the resultingfoam may be varied. The same applies to start of the rise and the risetime of the foaming. Nopcofoam H-103N supplies a rigid foam of about 3p.c.f. and H-102N supplies a rigid foam of about 2 p.c.f.

The foaming instructions are as follows for Nopcofoam H-102N: Thetemperature of both components should not be higher than about 70-75 F.The mixing ratio is about 52% R and 48% T, by Weight. The R component ispoured into the T component in the proper weight ratio. This is followedby mixing with a high speed drill motor, having a minimum RPM of 1800,using proper mixing blades, such as an impeller type. Mixture becomescreamy white and volume increase is noticed in about 25 to 30 seconds.The shell, acting as a mold, may advantageously be preheated to to F.This is advantageous particularly where the foam has to fill areas ofsmall cross-section. The higher the temperature the more rapid thefoaming action. The foam cures at room temperature in about 24 hours.

The foaming instructions for Nopcofoarn H-IOGN are similar to those ofH-102N with regard to temperature, mixing, mixing time, and curing.However, the mixing proportions of the components are about 50%R-component and about 50% T-component, by weight. The average coredensity is 2.6 p.c.f.; the K Factor, Aged (B.t.u./ hr./ sq. ft./ F./in.thick) is 0.120; maximum rec ommended service temperature is F.

Preparation of carbon dioxide blown rigid foams is illustrated by firstpreparing a prepolymer in two steps. In the first step the followingmaterials are added in the order shown to a clean and dry 12-literflask; 240 weight parts of tolylene diisocyanate (80/20 mixture of2,4/2,6 isomers) and 100 weight part of Pluracol TP 440 Triol, urethanegrade with hydroxyl number of 400. The Pluracols are polyoxypropylenederivatives of trimethylolpro pane, supplied by Wyandotte ChemicalsCorporation. They are available with varying molecular Weights and theyare characterized by their hydroxyl numbers. The one used herein has aviscosity of 625 cps. at 25 C. and an approximate molecular weight of418. As the above materials are mixed, the temperature rises due to anexothermic reaction. After the temperature rise subsides, thetemperature is adjusted to 100 C. and the mixture is held for 1 hour. Inthe second step the mixture is cooled to 60 C. and transferred to aclean and dry container for storage. The NCO/OH ratio of the product is3.85/ 1.0. After aging for 24 hours the viscosity of this prepolymer at25 'C. is 4000 cps.- 1000 cps. and it has a free -NCO content of 25%10.4%. For the Foam Preparation the following ingredients are firstpremixed:

For product I II Component 3.:

Above prepolymer (25% free NCO) 100 100 Silicone oil L-520 0.5 0.5Component B:

Diethylethanolamind. 1. O 1. 0 Water 2. 5 1. 5 Pluracol TP 440 25. 0 30.5 Quadrol polyol 6. 5 10. 0

free within 10 minutes. This type of foam is recommended to be cured forabout 2 hours at 70 C. By proper selection of faster catalysts thecuring temperature can be reduced even to room temperature. The coredensity for Product I is 1.8 p.c.f. and for Product II it is 2.8 p.c.f.The compressive strength at yield point in p.s.i. is 27.6 for Product Iand 49.0 for Product II.

The use of prepolymers can be illustrated by sprayable rigid urethanefoam systems. The foaming system consists of two fluid intermediateswhich are mixed immediately before application to the target surface.The intermediates are (a) a liquid prepolymer, prepared by reacting apolyol with an organic diisocyanate and (b) a liquid catalyst whichcontains (1) a volatile blowing agent and (2) a curing agent for thefoam. Component (a) is placed in a pressure tank. A heat exchanger inthe delivery line warms the prepolymer to 130 F. Compo nent (b) isthoroughly mixed and placed in a second pressure tank. A heat exchangermay also be used in this line to regulate its discharge temperature. Ina specially constructed spray gun, components are mixed externally inthe spray pattern after the materials leave the gun, but before theyreach the surface to be foam coated. The material begins foaming almostimmediately on the target surface, and rises to full foam height inabout 1 minute. The foam may be initially friable, but after curing,e.g. at 130 F. the friability disappears in 1015 minutes. Pluracol TP440 and Quadrol permit the formulation of this type of composition. Foamdensities of from about 2 /2 to about 3 p.c.f. are practical. Properformulation provides for elimination of sagging on vertical surfaces.The elevated temperature of the prepolymer also promotes prevention ofsagging.

In case of large scale production and where equipment cost permits it,one-shot application is of advantage. Polymethylenepolyphenylisocyanate, supplied under the trademark of PAPI by the UpjohnCompany, Polymer Chemicals Division, is suitable to illustratesuccessful one shot application for the pour-in-place or foam-in-placemethod of foam preparation. PAPI yields low exotherm one-shot systemspractical for conventional pour molding or spraying. It gives good earlystrength that allows quick handling of the end products. It has superiordimensional stability. Polyols suitable for use with PAPI includemethylglucoside, sorbitol, sucrose, amine-derived crosslinking agents,phosphorus-derived resins and polyesters. Suitable catalysts includetetramethylguanidine, trimethyl piperazine, dimethylethanolamine,triethylamine, dibutyltin dilaurate, stannous octoate, dibutyltindiacetate, amongst others. Suitable silicon co-polymers are Dow CorningCorporations DC-20l, Union Carbides L-520 and L-530 and GeneralElectrics X-F-1066. As blowing agents fluorocarbon 11 (F-ll) andinhibited F-ll, i.e. F11B are suitable for illustrative purposes. Otherfluorocarbons may also be used. Table 1 shows a few illustrativeexamples of PAPI based one-shot rigid urethane foams. Parts are byweight.

Silicone, D C201 Tetramethylguanidine Dimethylethanolamine 5Fluorocarbon 11B 38.0 41. PAPI (NCO/OH=1.05/l) 110.0 109. 0 Processing:

Resin component temp., F 110 105 PAPI component temp, F 110 115 Moldingtemperature, F 110 115 Overall density, pci 2. 45 2. 0

Formulation for non-self-extinguishing foam suitable for sprayapplication is given in Table 2.

22 TABLE 2 Weight parts PAPI 110.00 Polyfunctional polyglycol HydroxylNo. 450 100.00 Silicone DC-201 100.00 Silicone DC-201 2.00 Fluorocarbon11B 40.00 Tetramethylguanidine 2.00 DABCO (triethylenediamine) 1.50Dibutyltin diacetate 0.30

Precessing data NCO ratio 1.05 Resin stream temperature F 75 PAPI streamtemperature F 75 Throughput lbs/minute 5.50 Cream timeseconds 3 to 4Rise time-seconds 7 Tack free timeseconds 7 Core density-p.c.f 2 Closedcells percent As has been demonstrated, rigid polyurethane foam layerscan be prepared according to this invention by either one of the majorknown methods: (1) quasi-prepolymer method, (2) prepolymer method and(3) the one-shot method. The quasi-prepolymer method is preferred. Theapplication by poured-in-place or foamed-inplace method is satisfactory.Spray application is usable. Slush casting or rotational casting may beused in many instances.

The products of this invention require special care in many respects.Foaming and curing at temperatures where the molded skins do not deformhave an advantage and permit the elimination of the use of an outsidemold during foaming. It increases ease and economy of production iffoam-in-place filling of shells can be accomplished while the fillinghole of the mold remains open to the atmosphere. Conversely, the closingof molds and introducing pressures above 15 lbs. per square inch becomesmore difficult and less attractive.

With regard to shrinkage, no problem arises after curing if the innerlayer foam shrinks at the same rate as the shell. If the foam shrinks ina different degree and particularly if it shrinks more than the shellafter the molding operation is completed, an unacceptable product may beobtained. Therefore, preventive methods of manufacture are warranted toblock excessive shrinkage of the foam and formulation is adapted toavoid excessive shrinkage. During the period that the foam risespressure is exercised by the foam. To prevent deformation of the moldedskin caused by such excessive presure is also important. In some casesthe shells are backed up by a mold during the foaming operation toprevent such deformation. Proper formulation of the foaming compositionscan contribute greatly to the solution of these problems. However, inmany instances manufacturing steps or mechanical means are used toovercome possible difficulties. Some of these are discussed below inconnection with the drawings.

Whereas in most cases the rigid foam snugly attaches itself to themolded shell, in some cases it is of advantage to apply an adhesivelayer between the shell and foam to overcome possible effects ofexcessive shrinkage. A great variety of adhesives may be used. Hotasphalt or other hot adhesives are illustrative. Suitable adhesive typesare further illustrated by resorcinol adhesives, rubber emulsions,rubber solutions, epoxy resins, polyester resins, latex, latex modifiedcements, amongst others. The adhesive causes the shell either to shrinkwith the foam or, providing the shell is strong enough, the adhesivecauses the foam to adhere to the surface of the shell and prevents theformer from shrinking away from the surface.

A special type of foaming is known in the art as frothing. It is appliedby mixing machines, using Freon 12 23 (CCl F as blowing agent. Becauseof the low boiling point of this blowing agent, it is applied by a thirdline leading from a cooled pressure tank to the mixing head of themachine. A part of the foaming occurs in the mixing head and the rest inthe piece or mold. The percentual distribution between foaming in thehead and in the piece can be regulated by formulation. A 50:50percentual proportion is illustrative. Frothing falls under the terms ofpour-in-place and in situ foaming. It is characterized by lower foamrise and development of a lesser pressure during the foaming-in-placeoperation. As a consequence, it causes less distortion of the shellcomponent. Frothing is harder to control than other conventionalfoaming. It may simultaneously develop small and large cells, therebycausing some uneven material. The method is more adaptable to formlarger objects with large foam volumes. The difliculty of starting andstopping this type of operation, with equipment available at thepresent, more or less excludes it from the useful range of making smallobjects. Frothing can yield lower rigid foam densities than attainableby other methods.

After reviewing some of the considerations, further above it is apparentthat the absence of need for a second mold during foaming is of greatadvantage. Some of the advantages may be summarized as follows: (1) Easeof production of the composite articles of manufacture; (2) possibilityof producing composite articles of manufacture with complicatedundercuts which could not be removed from a one-piece or multi-piecesecond mold with the required ease; and (3) savings of the requiredlabor and mold cost. According to this invention many factors may assistto eliminate the need for a reinforcing mold during the foaming step.One factor is the proper and correct formulation of the foamingcomposition to achieve radical lowering of the foaming pressure. Thepressures of foams in rising can vary considerably. If excessivepressure develops, distention and distortion of the premolded shellcomponent may occur. Proper formulation achieves minimal shrinkage,minimal pressure development during foaming and low polymerizationtemperatures. With such a composition the foaming-in-place operation canbe carried out with ease without the application of a reinforcing moldduring the foaming operation. Another factor is to increase theresistance of the shells to distorting pressure by, for example,increasing the wall thickness of the shells or utilizing more rigidtypes of plastisol, such as those containing reactive acrylic monomers.The latter type yields shells which are still thermoplastic and pliable,but their deformation temperature is raised to a range of from about 138-F. to about 150 F. As they are considerably more rigid at roomtemperature than other more conventional plastisols, they have a greaterresistance to foam pressures without showing distortion. Still anotherfactor is the size of the access opening. In many instances where theshape and planned use of the composite article of manufacture permitsthe increase of the relative size of the access opening, such increasereduces the foaming pressure and permits the elimination of the secondor reinforcing mold during the foaming step.

Generally speaking requirement for a second reinforcing mold during thefoam-in-place operation exists where the composite article ofmanufacture is large in size, (like when it exceeds in one dimension 1or 2 feet), or has numerous flat surfaces. Even in cases of large shellsand shells that are particularly pliable, due to formulation orcomparatively thin wall thickness, I have found it possible to avoid theneed for a second mold by slush casting or rotational casting ofincremental layers of rigid polyurethane foam against the interior shellsurface. By applying several layers of comparatively thin coats of foamin succession a thick enough rigidifier component can be produced tomeet the requirements. No excessive pressure builds up and as aconsequence distortion is avoided. A similar elfect can be obtained byplacing a core in the interior of the shell cavity and foaming-in-placebetween the core and the interior surface of the shell. The core may beof a plastics skin or paper-chipboard, amongst others. The pressuresexerted are lowered in this case by the reduced volume and' thickness ofthe foam wall between the shell and the core. In a related embodimentincremental horizontal successive filling of foam layers is applied andas a result the distorting or distending pressure of the foam on theshell is reduced to a degree elimimating the need for a reinforcing moldduring foam application.

ANCILLARY REINFORCING ELEMENT (SPINE) When the outer shell component andthe inner rigid ifier component jointly form a cavity the presence of anancillary reinforcing element may be useful and desirable. Its utilityoccurs when the composite article of manufacture is exposed to strongstresses and pressures. Such an ancillary reinforcing element assiststhe rigidifying action of the inner component and toughens the compositearticle of manufacture. In my prior applications this element was calledreinforcing spine. This ancillary reinforcing element may be of metal,paper-chipboard, cardboard or a synthetic resin layer, amongst othersuitable materials. The element may be continuous or discontinuous. Whenit is continuous, it may be applied by casting, such as slush casting orrotational casting. Low melting point metal alloys, used as ancillaryreinforcing elements, may be applied by casting. The same applies to thesuitable synthetic resin compositions, llustrated by polyester resinsand essentially flexible epoxy resins. In many instances, mctals with amelting point of around 700 F. may be successfully cast into cavitiesformed jointly by outer and inner components. This can be explained bythe cooling action of the system forming the joint cavity on the castthin metal layer required.

The epoxy resins and polyester resins coat the entire interior surfaceof the joint cavity and are advantageously applied by casting. Theyimprove to a great extent the resistance of the composite articles ofmanufacture to the following stresses: impact, flexing, compression andtension. A few illustrative examples of suitable compositions to formsuch anciliary reinforcing elements (A-R-E) from synthetic resins aregiven below: (Percentages are by weight.)

Example A-R-ENo. 1: 12.4% of Laminac Polyester Resin #4128, 37.2% ofLaminac Polyester Resin EPX- 126-3, 0.1% cobalt naphthenate with 6%metal content, 49.3% flint (silica) 325 mesh grade and 1% of MEKperoxide, totaling 100%. This composition can be slush cast at roomtemperature and it sets in about 10 to 15 minutes. By reducing thequantity of cobalt and MEK peroxide the setting time can be extended.

Example A-R-ENo. 2: Example A-R-ENo. 1 is repeated with the change thatthe resin component is entirely 49.6% of Laminac Polyester ResinEPX-l26-3, the other ingredients remaining unchanged. This compositionproduces a more flexible resin layer than the preceding example and ispreferred. Some of the ingredients are described in greater detail underthe Shell Components under Example D.

position is made of the following ingredients: 15.05%

Epon Resin 871, 15.05% Epon Resin 828, 6.15% Epoxide #7 (an epoxyplasticizer of Procter & Gamble), 30.2% of 325 mesh grade silica, 30.2%of 60 mesh grade silica, 3.0% dimethyienetriamine (DTA) and 0.35%Cab-O-Sil, totaling Some of the ingredients are described in greaterdetail in Example C. of the shell component. The Cab-O-Sil regulatesviscosity, flow and stoppage of flow.

An illustration of desirable thickness for the resinous ancillaryreinforcing elements is from about 15 /2 mils to about 250 mils. Many ofthe resinous compositions can be applied by spraying.

In the drawings:

FIG. 1 is a vertical cross-sectional view of a single piece moldutilized in the present invention to prepare the shell portion. 13 isthe metal mold and it shows an undercut.

FIG. 2 is a vertical cross-sectional view of the mold of FIG. 1. Shell14 is molded in mold 13.

FIG. 3 is a vertical cross-sectional view of the mold 13 of FIG. 1,illustrating the removal of the plastisol shell 14 from the mold. Theshell is in a somewhat collapsed and distorted state at the removaltemperature, but regains its original molded shape after removal andcooling to room temperature.

FIG. 4 shows the plastisol shell 14 after removal from the metal mold 13according to FIG. 3. Rigid foam 15 fills out the cavity of the moldedshell 14. The shell is protected during the foaming operation by aplaster of paris mold 16 which has been applied to the molded shelle.g., b dipping, prior to foaming. For this purpose the shell is dippedin a liquid plaster mixture, providing contact between the outsidesurface of the shell and the plaster mixture. The plaster mixture isallowed to solidify. The foaming composition is then placed into thecavity of the shell and allowed to foam-in-place.

FIG. 5 shows the vertical cross-sectional view of the composite articleof manufacture of FIG. 4, with the shell 14 and the rigid foam 15, afterthe plaster of paris mold of FIG. 4 has been removed by cracking andpeeling.

It may be noted, that in FIG. 4 low temperature melting metal alloys,such as manufactured by the Cerro Corporation, can be sprayed on theshells, to replace the plaster of paris layer. After the rigid foamcomposition solidifies and cures in the cavity of the shell the metalcan be melted off at low temperatures and recovered. This alternativerequires proper correlation between the. melting point of the lowtemperature melting metal alloy and the maximum temperature to which theshell material can be exposed to without permanent damage.

FIG. 6 is identical with FIG. 5 of the copending parent application Ser.No. 22,002 referred to above and illustrates the verticalcross-sectional view of an article manufactured according to thisinvention. 14 is the molded plastisol shell. 15 is a rigid polyurethanefoam inner rigidifier component which fills out the cavity of the moldedplastisol shell. 17 illustrates weights which are suspended in the rigidpolyurethane foam. They serve to reduce the quantity of the requiredpolyurethane foam, reduce shrinkage and may also increase the weight ofthe composite article of manufacture. The inexpensive scrap weights areselected from products having suitable density and may be illustrated bwood scrap, such as wood ends from boards cut into cubes, or cardboardobjects of various shapes. These scrap pieces are placed into the cavityof the molded shell prior to solidification of the rigid foam eitherprior to pouring of the foam composition or shortly thereafter. They mayalso be premixed with the foam composition or one of its components. Auniform distribution of these weights in the foam composition isdesirable. This goal can be achieved with ease.

FIG. 7 illustrates a vertical cross-sectional view of a compositearticle of manufacture of this invention at the manufacturing stage. 18illustrates a two-piece mold in which the plastisol shell 14 is molded.15 is the rigid polyurethane foam. The shell is kept in place in themold while the composition forming the rigid polyurethane foam ispoured-in-place and foamed-in-place in the molded shell. The compositearticle of manufacture is removed from the mold only after themanufacturing is fully completed and the foam is cured. For removal, thetwo-piece mold is taken apart. To facilitate removal, the mold surfacemay contain a mold release lubricant, or air pressure may be appliedbetween mold surface and shell.

FIG. 8 illustrates a vertical cross-sectional view of a compositearticle of manufacture of this invention. 14 is the molded outer shellcomponent. 19, 20 and 21 illustrate three individual layers of rigidpolyurethane foam, applied and formed in succession. To secure evendistribution they are poured-in-place in subsequent increments, each onecoating the inner surface of the available inner cavity while the shellis being rotated and the foam forming composition is still liquid. 19coats the inner surface of the shell. 20 coats the inner surface of 19and 21 coats the inner surface of 20. In some cases it is advantageousto complete the distribution of the foam forming composition on theinterior surface of the cavity prior to commencement of the foaming. Theindividual layers of the solid polyurethane foam have good adhesion toeach other. The embodiment illustrated by FIG. 8 reduces the quantity ofpolyurethane foam utilized, reduce shrinkage and, by reducing thepressure during the foam expansion, eliminates the need for an outsidemold during the foaming operation in the majority of the cases. In oneembodiment of this invention, as illustrated by FIG. 8, 19 is a foam ofabout 20 to 25 p.c.f. and 20 and 21 are of a foam of about 2 to 3 p.c.f.The high density foam performs the main task of rigidification andprevents distortion during the second and third foaming step without theuse of a mold during foaming. In another embodiment all three layers of19, 20 and 21 are of a foam of about 1 /2 to 3 p.c.f. In FIG. 8 theouter shell component and the inner rigidifier component jointly form acavity.

FIG. 9 is an alternative form of FIG. 8. The additional feature is 22,illustrating an ancillary reinforcing element on the interior surface ofthe cavity formed jointly by the outer shell component and the threelayers of the inner rigidifying component. In this instance theancillary reinforcing element is advantageously either a flexible epoxyresin composition or a flexible polyester composition. They can beapplied by slush casting or rotational casting or by spray application.They are of a composition which cures either at room temperature or atlow elevated temperatures.

FIG. 10 is a front view of a three-dimensional illustration of acomposite article of manufacture of this invention, having both verticaland horizontal rectangular cross-sections. This type of object has agreater tendency to push outward during foaming as a consequence of thefoam rise. 19, 19-a, 19-b, 20, 20-a, 20b, 21, 21-a and 21-h illustrate 9individual layers of rigid polyurethane foam, prepared as described inconnection with FIG. 8 in successive foaming steps. This layer methodelimina-tes the excessive pressure during foaming and simultaneously mayeliminate the need for an outer protective mold during the foaming.

FIG. 11 is a vertical cross-sectional view of a composite article ofmanufacture according to this invention. 14 is the molded shell. 23 is atube placed into the internal cavity of the molded shell. This tube canbe made e.g. of thin aluminum metal, or of chipboard paper or the like.The rigid polyurethane foam 15 is formed around the tubing. The effectis to reduce the inward shrinkage of the foam layer and also to reducethe quantity of polyurethane foam used.

FIG. 12-A and FIG. l2-B illustrate alternatives. They are verticalcross-sectional views of related and alternative composite articles ofmanufacture of this invention. 14 is a molded plastisol shell. 24 is athin layer of molded plastics skin protruding into the internal cavityof the molded shell 14. During the foaming operation this thin layer of24 can be supported by a plug 25 which is then withdrawn after thefoaming operation is completed.

a is a rigid polyurethane foam which has been prepared by foaming aroundthe plastic coated plug. The foam 15-a fillls out the space between thesaid plastics coated plug and the molded outer shell component. Afterthe foaming producing 15-a is completed, according to the alternativeillustrated by FIG. 12-A, the plug is removed, leaving the thin layer ofplastics slrin 24 as a coating on the interior of the cavity of the foamlayer 15-11. This illustrates the utility for insulated containers, likethermos bottles. In another alternative, illustrated by FIG. l2-B, boththe plastics skin 24 and the plug 25 of FIG. l2A are withdrawn and thespace obtained by such withdrawal is filled with a second quantity ofrigid polyurethane foam 154). This second quantity of foam 15-b issupported by the outer foam layer of 15a during the foaming operation.In this last mentioned embodiment, illustrated by FIG. 12-B, 15-a may beof a rigid higher density polyurethane foam with p.c.f. values of fromabout to about 25, whereas 15b may have a p.c.f. value of from about 1%to about 3. The high density foam performs the main task ofrigidification andprevents distortion in the second foaming step withoutthe use of a mold.

The drawings illustrate some aspects of this invention and do not limitthe scope of the invention herein claimed.

I claim:

1. The process for producing a rigid impact resistant composite articleof manufacture comprising a hollow outer shell component which has anaccess opening to its cavity and a cellular inner rigiditier component,said process comprising the sequence of the steps of (a) molding in asingle hollow female mold a unitary substantially void-free andjointless hollow single shell component having an access opening to itscavity of a flexible pliable resilient thermoplastic organic plasticsmaterial, said molding step being carried out to completion to producethe shell molded to its final physical strength and texturallydecorative characteristics, thus permitting removal of the shellcomponent from its mold, said shell component being free of an undercut,said thermoplastic organic plastics material selected from the groupconsisting essentially of (i) vinyl chloride in a polymerized andplasticized state, (ii) vinyl chloride and a reactive acrylic monomer ina polymerized and plasticized state, (iii) ethylene in a polymerizedstate, (iv) propylene in a polymerized state, (v) ethylene and vinylacetate in a copolymerized state, (vi) ethylene and ethylacrylate in acopolymerized state, (vii) methylmethacrylate in a polymerized state,(viii) polycarbonates, (ix) ethyl cellulose, (x) cellulose acetate, and(xi) cellulose acetobutyrate,

(b) preparing, in a separate step, a foam forming liquid organicplastics composition able to form a rigid cellular structure in situ inthe premolded shell component obtained in step (a), said rigid cellularstructure when formed and set being a rigid foam selected from the groupconsisting essentially of (1) rigid polyurethane foams, (2) rigid epoxyfoams, (3) rigid polyvinyl chloride resin foams, (4) rigid phenolicresin foams, (5) rigid urea-formaldehyde foams, (6) rigid polyesterfoams, (7) asphalt foams, (8) hard rubber foams, (9) rigid siliconefoams, (l0) rigid acrylic foams prepared from alpha-chloroacrylic acidester polymers and (11) rigid syntactic foams,

(c) introducing said liquid organic plastics composition into the cavityof the premolded shell component through its access opening,

(d) causing said liquid organic plastics composition to foam-in-placeinside the cavity of said shell component,

(e) solidifying the cellular structure so formed and (f) recovering therigid composite article of manufacture so produced,

28 said steps (c), (d) and (e) providing the cellular rigidifiercomponent to be in intimate contact with the entire inner surface of theouter shell component.

2. The process of claim 1, wherein the liquid organic plasticscomposition in (c) is poured into the cavity of the hollow shellcomponent.

3. The process of producing a rigid impact resistant composite articleof manufacture comprising a hollow outer shell component which has anopening to its cavity and a cellular inner rigidifier, said processcompris'mg the sequence of the steps of (a) molding in a single hollowfemale mold a unitary substantially void-free and jointless hollowsingle shell component having an access opening to its cavity of athermoplastic pliable resilient organic plastics material in a manner toyield an outer shell component with a wall thickness from about 15.5mils to about 250 mils, said molding step being carried out tocompletion to produce the shell molded to its final physical strengthand texturally decorative characterlistics, thus permitting removal ofthe shell component from its mold if so desired, said shell componentbeing free of an undercut, said thermoplastic organic plastics materialselected from the group consisting essentially of (i) vinyl chloride ina polymerized and plasticized state, (ii) vinyl chloride and a reactiveacrylic monomer in a polymerized and plasticized state, (iii) ethylenein a polymerized state, (iv) propylene in a polymerized state, (v)ethylene and vinyl acetate in a copolymerized state, (vi) ethylene andethylacrylic in a copolymerized state, (vii) methylmethacrylate in apolymerized state, (viii) polycarbonates, (ix) ethyl cellulose, (x)cellulose acetate, and (xi) cellulose acetobutyrate,

(b) removing the molded shell component from its mold,

(c) preparing, in a separate step, a foam forming liquid organicplastics composition able to form a rigid cellular structure in situ inthe premolded shell component, said rigid cellular structure when formedand set being a rigid foam selected from the group consistingessentially of (l) rigid polyurethane foams,

(2) rigid epoxy foams, (3) rigid polyvinyl chloride resin foams, (4)rigid phenolic resin foams, (5) rigid urea-formaldehyde foams, (6) rigidpolyester foams,- (7) asphalt foams, (8) hard rubber foams, (9) rigidsilicone foams, (10) rigid acrylic foams prepared fromalpha-chloroacrylic acid ester polymers and (11) rigid syntactic foams.

(d) introducing said liquid organic plastics composition into the cavityof the premolded shell component through its access opening,

(e) causing said liquid organic plastics composition to foam-in-placeinside the cavity of the shell component,

(f) solidifying the cellular structure so formed, and

(g) recovering the rigid composite article of manufacture so produced,

said steps (d), (e) and (f) providing the cellular rigidifier componentto be in intimate contact with the entire inner surface of the outershell component.

4. The process of producing a rigid composite article of manufacturecomprising a flexible pliable and resilient hollow single outer shellcomponent which has an access opening to its cavity and a cellular innerrigidifier component, said process comprising the sequence of the stepsof (a) casting plastisol in a seamless single female die,

(b) heating the plastisol to gelation temperature,

(0) fusing the gelled plastisol layer to form a tough and substantiallyvoid-free jointless premolded outer shell component, said fusion stepbeing carried out to completion to produce the shell molded to its finalphysical strength and texturally decorative char- 29 acteristics, saidshell component being free of an undercut,

(d) stripping the premolded shell component from the die,

(e) preparing, in a separate step, a foam-forming liquid organicplastics composition able to form a rigid cellular structure in situ inthe premolded shell component, said rigid cellular structure when formedand set being a rigid foam selected from the group consistingessentially of (1) rigid polyurethane foams, (2) rigid epoxy foams, (3)rigid polyvinyl chloride resin foams, (4) rigid phenolic resin foams,(5) rigid urea-formaldehyde foams, (6) rigid polyester foams, (7)asphalt foams, (8) hard rubber foams, (9) rigid silicone foams, (10)rigid acrylic foams prepared from alpha-chloroacrylic acid esterpolymers and (11) rigid syntactic foams,

(f) pouring said foam forming liquid organic plastics composition intothe cavity of the premolded shell component through its access opening,

(g) causing said liquid organic plastics composition to foam-in-placeinside the cavity of the shell component,

(h) solidifying the cellular structure so formed while providing thecellular rigidifier component to be in intimate contact with the entireinner surface of the outer shell component, and

(i) recovering the rigid composition articles of manufacture soproduced,

said steps (f), (g) and (h) carried out in a manner to deposit a rigidfoam in intimate contact with the entire inner surface of the hollowouter shell component, the wall thickness of said deposit beingsuflicient to prevent the deformation of the shell component by handpressure, thereby rigidifying the hollow shell component in itsentirety, said plastisol being a dispersion of a polyvinyl resin inliquid organic plasticizers and said polyvinyl resin comprising vinylchloride in a polymerized state.

5. The process of claim 4, wherein the outer shell component formed bysteps (a), (b), and (c) has a wall thickness of from about 15.5 mils toabout 250 mils.

6. The process of claim 4, wherein the plastisol outer shell componentis prepared by slush casting and any excess of plastisol is poured offprior to the fusion step (c).

7. The process of claim 4, wherein the plastisol outer shell componentis prepared by rotational casting.

8. The process of claim 3, wherein the liquid organic plasticscomposition prepared in step (c) is a prepolymer composition yielding arigid polyurethane foam structure.

9. The process of claim 3, wherein the liquid organic plasticscomposition prepared in step (c) is a quasi-prepolymer compositionyielding a rigid polyurethane foam structure.

10. The process of claim 3, wherein steps (c), (d), (e), and (f) arecarried out in a way to bring about filling of the cavity of the outershell component with the rigid cellular structure in its entirety.

11. The process of claim 3, wherein step (d) is carried out by castingand steps ((1), (e) and (f) bring about the lining of the inner surfaceof the outer shell component with a layer of the rigidifier component,thereby jointly forming a cavity of the shell component and therigidifier component, said rigidifier being in intimate contact with theentire inner surface of the outer shell component.

12. The process of claim 3, wherein step (d) is carried out by castingand steps (d), (e) and (f) bring about the lining of the inner surfaceof the outer shell component with a layer of the rigidifier component,thereby jointly forming a cavity of the shell component and therigidifier component, said rigidifier component being in intimatecontact with the entire inner surface of the outer shell component and,in an additional step, depositing a room temperature setting resinouscomposition of the inner surface of said joint cavity, said resinouscomposition being a member of the class consisting of room temperaturesetting flexible epoxy resins and room temperature setting flexiblepolyester resins and setting the cast resinous composition.

13. The process of claim 1, wherein a layer of adhesive is applied tothe inner surface of the outer shell component prior to introducing theliquid organic plastics composition forming the rigid cellular structureinto the cavity formed by said outer shell component, said adhesivehaving good adhesion both to the plastics of which the outer shell ismolded and to the rigid foam of the inner rigidifier component.

14. The process of claim 1, wherein the outer shell component is in amulti-piece mold during the formation of the inner rigidifier component.

15. The process of claim 3, wherein steps (c), (d), (e), and (f) arecarried out by slush casting in a way to bring about the lining of theinner surface of the outer shell component with a layer of therigidifier component, thereby jointly forming a cavity of the shellcomponent and the rigidifier component, said rigidifier component beingin intimate contact with the entire inner surface of the outer shellcomponent.

16. The process of claim 3, wherein steps (c), (d), (e), and (f) arecarried out by rotational casting in a way to bring about the lining ofthe inner surface of the outer shell component with a layer of therigidifier component, thereby jointly forming a cavity of the shellcomponent and the rigidifier component, said rigidifier component beingin intimate contact with the entire inner surface of the outer shellcomponent.

17. The process of claim 3, wherein steps (c), (d), (e), and (f) arecarried out in a way to bring about the incremental lining of the innersurface of the outer shell component with successive layers of therigidifier component, the first layer of said rigidifier component beingin intimate contact with the entire inner surface of the outer shellcomponent, said step (a) being carried out by casting.

18. The process of claim 3, wherein steps ((1), and (e) are carried outin the premolded shell component per so, while the latter is free of thesupport of a reinforcing mold, and said steps (d), (e), and (f) arecarried out at ambient temperatures.

19. The process of claim 3, wherein steps (d), (e), and (f) are carriedout in the absence of a mold and in a manner to form successivehorizontal layers inside said cavity, until the cavity is substantiallyfilled.

20. The process of claim 1, wherein in step (c) the introducing of theliquid organic plastics composition into the cavity of the premoldedshell component through its access opening is carried out by spraying.

21. The process of producing a rigid impact resistant composite articleof manufacture comprising a hollow outer shell component which has anopening to its cavity and a cellular inner rigidifier component, saidprocess comprising the sequence of the steps of (a) molding in a singlehollow female mold a unitary substantially void-free and jointlesshollow single shell component having an access opening to its cavity ofa thermoplastic pliable resilient organic plastics material, saidmolding step being carried out to completion to produce the shell moldedto its final physical strength and teXturally decorativecharacteristics, thus permitting the removal of the shell component fromits mold, if desired, said shell component being free of an undercut,said thermoplastic organic plastics material selected from the groupconsisting essentially of (i) vinyl chloride in a polymerized andplasticized state, (ii) vinyl chloride and a reactive acrylic monomer ina polymerized and plasticized state, (iii) ethylene in a polymerizedstate, (iv) propylene in a polymerized state, (v) ethylene and vinylacetate in a copolymerized state, (vi) eth- 31 ylene and vinyl acetatein a copolymerized state, (vi) ethylene and ethylacrylate in acopolymerized state, (vii) methylmethacrylate in a polymerized state,(viii) polycarbonates, (ix) ethyl cellulose, (x) cellulose acetate, and(xi) cellulose acetobutyrate,

(b) preparing, in a separate step, a polystyrene composition suitable toform a rigid cellular structure in situ in the premolded shellcomponent,

(e) introducing said polystyrene composition into the cavity of thepremolded shell component through its access opening, while the shell isin a supporting mold,

(d) causing the polystyrene composition to foam-inplace inside thecavity of the shell component,

(e) solidifying the cellular structure so formed, and

(f) recovering the rigid composite article of manufacture so produced,

said steps (d) and (e) providing the cellular rigidifier component to bein intimate contact with the entire inner surface of the outer shellcomponent, thereby rigidifying the hollow shell component in itsentirety and preventing the deformation of the shell component by handpressure.

22. The process of claim 21, wherein in step (c) the supporting mold isthe same mold in which the outer shell component was molded.

23. The process of claim 21, wherein in step (c) the supporting mold isa second mold which is different from that used in molding the outershell component, and the premolded shell component is removed from itsmold prior to introducing the polystyrene composition into its cavity.

32 References Cited UNITED STATES PATENTS 3,091,946 6/1963 Kesling 264-X 2,753,642 7/1956 Sullivan 264-45 X 3,283,386 11/ 1966 Cenegy 264-453,198,864 8/ 1965 Bingham 264-250 1,998,897 4/1935 Kay 264-310 2,974,3733/1961 Streed 264-45 3,133,853 5/1964 Knox 264-45 X 2,787,809 4/ 1957Stastny 264-53 3,163,686 12/1964 Dusel 264-45 2,950,505 8/1960 Frank264-45 3,112,987 12/1963 Griffiths 264-45 2,939,180 6/ 1960 Hickler etal 264-302 X 2,948,651 8/ 1960 Waag 264-45 X 2,977,639 4/ 1961 Barkhufiet al 264- X 3,246,069 4/1966 Maynard 264-310 X 3,390,214 6/1968 Woods264-45 3,410,934 11/ 1968 Kuritzkes et al. 264-310 X 3,493,257? 2/1970Fitzgerald et al. 264-45 X 3,623,931 11/1971 Van Hosen 264-45 X3,705,222 12/1972 Rogers et a1. 264-45 FOREIGN PATENTS 873,518 7/ 1961Great Britain 264-45 X OTHER REFERENCES Hackhs Chemical Dictionary, 3rded., McGraw-Hill, New York (1944), P- 34. Call No. QD'5H3.

HERBERT S. COCKERAM, Primary Examiner US. Cl. X.R. 264-53, 310

